Numerous industrial, mechanical and household products require that patterns be cut into their metal surfaces. Included among such applications are metal lids that permit the diffusion of scented air from a container through a cut-out design. Such designs are commonly stamped through the top wall of the lids by a punch press apparatus. A typical press includes a die and a punch that is hydraulically moved along an axis perpendicular to the die. The punch features raised portions that mate with corresponding recesses in the punch. The mating surfaces of the die and punch correspond to the apertured design required for a given application.
During stamping, the mating portions of the die and punch shear through an interposed metal lid or sheet. More specifically, the metal workpiece is placed directly onto the die prior to stamping. As the punch is lowered and made to mate with the die, it cuts through the metal sheet as disclosed in U.S. Pat. No. 3,388,841. Elastic or laminate layers are optionally positioned between the punch and the metal workpiece to absorb tensile stresses incurred by the metal and die. Such a configuration is disclosed in U.S. Pat. No. 4,829,807.
Conventional stamping methods such as those above cause sharp edges to be formed along their stamped designs. Such exposed edges present safety concerns to assemblers and consumers. Further, known stamping techniques severely weaken the structural integrity of the lids by cutting away supportive portions of metal. Consequently, designs requiring a substantial portion of the lid to be removed are not feasible. Thus, in applications such as are described above, there is a need for an apparatus and method for stamping apertured designs into metal without substantially weakening the metal surface and exposing sharp edges.